Subscriber access provided by UNIV OF CAMBRIDGE
Article
Single-step Assembly of Multifunctional Poly Tannic Acid-Graphene Oxide Coating to Reduce Biofouling of Forward Osmosis Membranes Hanaa M. Hegab, Ahmed Elmekawy, Thomas Geoffrey Barclay, Andrew Michelmore, Linda Zou, Christopher P Saint, and Milena Ginic-Markovic ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b03719 • Publication Date (Web): 13 Jun 2016 Downloaded from http://pubs.acs.org on June 15, 2016
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
Single-step Assembly of Multifunctional Poly Tannic AcidGraphene Oxide Coating to Reduce Biofouling of Forward Osmosis Membranes Hanaa M. Hegab a,b, Ahmed ElMekawy c,d, Thomas G. Barclay e, Andrew Michelmore e, Linda Zou a,f, Christopher P. Saint a, Milena Ginic-Markovic e,* a
Natural & Built Environments Research Centre, University of South Australia, Adelaide, SA 5095, Australia
b
Institute of Advanced Technology and New Materials, City of Scientific Research and Technological Applications,
Borg Elarab, Alexandria, Egypt c
Genetic Engineering and Biotechnology Research Institute, University of Sadat City (USC), Sadat City, Egypt
d
School of Chemical Engineering, University of Adelaide, Adelaide, Australia
e
Future Industries Institute, University of South Australia, Adelaide, SA 5095, Australia
f
Department of Chemical and Environmental Engineering, Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates.
ABSTRACT Graphene oxide (GO) nanosheets have anti-bacterial properties that have been exploited as a biocidal agent used on desalination membrane surfaces in recent research. Nonetheless, improved strategies for efficient and stable attachment of GO nanosheets onto the membrane surface are still required for this idea to be commercially viable. To address this challenge, we adopted a novel, single-step surface modification approach using tannic acid cross-linked with polyethylene imine as a versatile platform to immobilize GO nanosheets to the surface of polyamide (PA) thin film composite (TFC) forward osmosis (FO) membranes. An experimental design based on Taguchi’s statistical method was applied to optimize the FO processing conditions in terms of water and reverse solute fluxes. Modified membranes were analyzed using water contact angle (WCA), adenosine triphosphate (ATP) bioluminescence, total organic carbon (TOC), Fourier transform infrared spectroscopy (FTIR), zeta potential, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). These results show that membranes were modified with a nanoscale (< 10 nm), smooth, hydrophilic coating that, compared to pristine membranes, improved filtration and significantly
Address correspondence to
[email protected] 1 ACS Paragon Plus Environment
ACS Applied Materials & Interfaces
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 37
mitigated biofouling by 33% due to its extraordinary, synergistic antibacterial properties (99.9%).
Keywords: Forward osmosis; tannic acid; graphene oxide; single-step multifunctional coating; anti-biofouling; Taguchi method.
I- INTRODUCTION Bacterial cells can survive in severe environments, including the extreme hydrodynamic conditions present in membrane filtration. Under these conditions, bacteria and other microbes form cohesive, stable biofilms on the membrane surfaces, reducing the water permeation rate and salt rejection, 1,2 hindering sustained, efficient filtration. 3–5 In spite of the earlier studies aimed at mitigation of biofouling, 6,7 a practical strategy for inhibiting biofilm formation on the membrane surface is still needed. One type of membrane filtration process for which fouling is one of the key bottlenecks is forward osmosis (FO). FO is based on the osmotic gradient difference between feed and draw solutions, and has great potential to purify brackish or waste-water using relatively low amounts of energy.
8,9
FO employs similar polyamide (PA) thin film composite
(TFC) membranes to those used in reverse osmosis, and for both applications the inherent physicochemical properties of the PA membranes support the adhesion of bacterial cells, leading to the development of biofilm on the membrane surface. 10,11 The recent wave of research on the unique attributes of biocidal graphene oxide (GO)
12–15
has highlighted an opportunity to tailor
TFC membrane surface properties to reduce biofouling. Although GO nanosheets have been used by many researchers to engineer the surface properties of membranes, a practical method for attaching GO nanosheets on the membrane surface is still considered a challenge.
15–18
There has been an explosion in research into the
nearly universally adhesive nano coatings using the catecholamine or polydopamine.
19,20
More
recent expansion of the development of catechol chemistry based coatings has used the environmentally friendly, cost effective polyphenol, tannic acid (TA). 21–26 For example, Sileika et al.
24
described the ability of TA to oxidatively polymerize to form coatings in a similar
fashion to polydopamine. At the same time, Ejima et al. 21 reported the development of a new TA coating using coordination complexes with ferric ions.
21–24
TA surface coatings created using
Address correspondence to
[email protected] 2 ACS Paragon Plus Environment
Page 3 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
these techniques have demonstrated free radical scavenging and antibacterial properties 24 as well as being used as an adhesive layer to attach other functional polymers such as PEG, the hybrid coating used to reduce marine biofouling. 26 Compared to polydopamine coatings, poly tannic acid (pTA) has advantages for the commercial application of anti-biofouling coatings as it is substantially less expensive and has partial bactericidal activity. 24 However, the durability of pTA films is problematic, ferric ion coordination complexes being degraded by relatively mild acidity 27 and tannic acid coatings have required a polydopamine surface primer to strengthen attachment,
21,26
and so increased
resilience is required for membrane filtration applications. The stability of both polydopamine 28 and catechol
29,30
oxidatively polymerized coatings are significantly improved through cross-
linking with polyethyleneimine (pEI). Based on this we have incorporated GO nanosheets into an adhesive coating using both TA and pEI. The branched pEI has an abundance of primary and secondary amines that can react with TA both through Schiff base and Michael addition reactions,
29
promoting the oxidative polymerization of TA.
31
Additionally, pEI amine groups
can form covalent linkages to epoxide groups on GO through addition reactions. Consequently, pEI has the capacity to cross-link the composite material, allowing strong adhesion to the PA membrane surface. In this work we optimize the GO concentration in a pEI-pTA composite coating, along with coating deposition time and draw solution concentration, using the Taguchi method, analyze the chemical and morphological structure of the resultant modified membranes and evaluate their filtration and antibiofouling performance. To the best of our knowledge this is the first example of the use of a TA and pEI to make a composite coating and the first incorporation of GO into a pTA based coating for anti-biofouling applications.
II-MATERIALS AND METHODS 2.1. Materials Graphite powder SP-1, size < 20 micron was purchased from Bay Carbon™ (USA). Hydrochloric acid (30%), sulphuric acid (98%), nitric acid (70%), hydrogen peroxide (30%), acetic acid (99.7%), potassium permanganate powder, tannic acid (TA), polyethyleneimine (PEI), bicine, sodium hydroxide, potassium chloride, sodium persulphate and phosphoric acid were purchased from Sigma-Aldrich™ (Australia). SW-TFC FO membrane (HTI-first generation, USA) were used in this study. Sodium chloride (analytical grade) and sodium acetate 3 ACS Paragon Plus Environment
ACS Applied Materials & Interfaces
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 37
were obtained from Ajax Finechem Pty Ltd (Australia). Sodium nitrate and sodium dihydrogen phosphate were procured from Merck (Australia), and May and Baker Ltd (England), respectively. MilliQ water (18.2 MΩ) from an ultrapure water purification system (Millipore, Synergy®) was used in all experiments.
2.2. Statistical Analysis Taguchi design was used to analyse the influence of GO concentration (µg/mL), coating deposition time (min) and draw solution concentration (M) on the membrane performance properties of water flux (Jw) and reverse solute flux (Js). 32 Analysis of variance (ANOVA) was employed to determine the significance of the chosen factors by Minitab software v.17. The experimental matrix is presented in Table S1. The optimum performance was obtained through measuring the quality of “smaller the better” (S/NS) and “larger the better” (S/NL) for Js and Jw, respectively, as defined according to Equations (1) and (2). 33,34 S/Ns = -10 log
/ = −10
∑
∑% # ! " $ &
#
(1)
'
(2)
Where n is the number of experiments and yi is the response of each experiment.
2.3. GO Synthesis and In-situ Single-step Surface Modification of Membranes GO nanosheets were synthesized from graphite using a modified Hummers technique
18
and applied to FO membranes using the modification procedure depicted in Figure 1. In brief, FO membranes were immersed in deionized water for at least 24 h before membrane modification. The FO membranes were then placed with the active side facing up between a poly methylmethacrylate backing plate and a neoprene gasket and topped with a poly methylmethacrylate open bottom container. The set up was clamped in place on a rockingplatform (RPM5, Ratek, Australia) using springs. This set-up was used to ensure only contact of the active surface of the membrane to the reaction solution. The reaction solution was prepared by dissolving PEI (2 g/L) in bicine buffer solution (50 mM, pH 7.8). GO nanosheets, with varying concentrations (40, 80, 120 µg/ml), were dispersed into a separate solution of TA (2
4 ACS Paragon Plus Environment
Page 5 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
g/L). The two solutions were then combined and added immediately to the reaction container. The reaction container was oxygenated (2 L/min) and agitated at 4 rpm for a range of deposition times, according to the
Figure 1. Schematic illustration for the coating formation of GO-pTA-pEI on the surface of a membrane via in-situ chemical modification reaction under oxygen.
5 ACS Paragon Plus Environment
ACS Applied Materials & Interfaces
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
experimental design matrix, creating membrane samples with designated names GO40, GO80 and GO120 for membranes with GO loadings 40, 80, 120 µg/ml.
2.4. Membrane Characterization Surface charge and hydrophilicity analysis Zeta potential measurements were performed using an Electrokinetic Analyser (Anton Paar, Austria) equipped with adaptable gap cell height. The wettability assessment was done via the captive bubble method in order to measure the contact-angle using Data Physics Instrument (GmbH, Filderstadt, Germany). The details of the analysis procedure are detailed in our previous study. 15
Morphological and topographical analysis GO and functionalized-graphene oxide (f-GO) nanosheets, along with the cross-sections of the pristine and modified membranes, were captured by transmission electron microscopy (FEI Tecnai G2 Spirit TEM) to analyse their morphologies. 35 The topography of the membranes were analysed by AFM using NT-MDT NTEGRA SPM in non-contact mode. To measure the dimension of GO and f-GO nanosheets, a few drops of GO and f-GO nanosheets dispersed in water (5 µg/mL) were deposited on a silicon wafer (1 cm2). 36
FT-IR spectroscopy attenuated total reflectance (ATR) and XPS analysis The surface chemistry of GO nanosheets, f-GO nanosheets, pristine and modified membranes were established using FT-IR spectroscopy (ATR) and XPS. FT-IR ATR was conducted using a Nicolet Nexus 8700 FTIR Spectrophotometer (Thermo Electron Corporation) equipped with a ‘Smart Orbit’ ATR accessory. Prior to sample analysis a background was collected, which was subsequently subtracted from sample spectra. In addition an automatic baseline rectification and scale normalization were applied for all data. Membranes samples were placed, with the active-side down, on the ATR crystal and fixed by a clamp. All sample spectra were obtained utilizing 256 scans in the range of 400-4000 cm-1 and a resolution of 4 cm-1, and the data was manipulated using Omnic software. XPS analysis was performed using a Kratos Axis-Ultra DLD X-ray photoelectron spectrometer (Kratos Analytical, Manchester, UK) utilizing a mono-chromated Al-Ka X-ray 6 ACS Paragon Plus Environment
Page 6 of 37
Page 7 of 37
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
source. Survey spectra were assimilated at 160 eV pass energy, in addition to C1s core-level spectra were acquired at 20 eV at a take-off angle of 90◦ according to the surface of the sample. The spectra were charge corrected via setting the aliphatic hydrocarbon element of the C1s at 285.0 eV and analyzed using CasaXPS software (Neal Fairly, UK). The surface quantification of the pristine and modified samples was performed using a linear background subtraction and manufacturer-supplied sensitivity factors, which integrate the known transmission function of the analyzer. Moreover, the curve fitting of the C1s region of membranes’ surfaces were accomplished using well-known Beamson and Briggs chemical shifts. 37
FO setup for membrane performance assessment All membranes including the pristine and coated membranes (surface area of 48 cm2) were assessed in FO mode, using customized FO setup to evaluate their performance in terms of water and reverse solute fluxes Jw, Js and biofouling resistance. Mesh spacers (Sterlitech) were positioned on both sides of the membrane housing. The feed solution was MilliQ water and draw solutions were prepared from MilliQ water using various sodium chloride concentrations based on the experimental design matrix. Both feed and draw solutions were circulated in each experiment using a peristaltic pump with a flow rate of 500 mL/min measured using a flow meter. The draw solution concentration was maintained during the experiment by using a conductivity sensor and dosing pump. The Js (mg/min) and Jw (L/m2 h) were calculated according to variation of salt concentration as a function with time and volume change of water permeation in the feed side, as indicated in Equation (3). 38 () = 60/73480 9.314:0 4304 × ∆
